Method of making self-lubricating filament wound tube

ABSTRACT

A method of making a filament wound tube having smooth surfaces. Fiber glass filaments are passed through successive resin baths containing particles of a wear resistant additive. These resin baths are deaerated to reduce the existence of voids and pits in the resin in the finished tube. The filaments are flattened and are slowly helically wound in a first layer onto a mandrel. Subsequent layers are overwound about the first layer, the resin is cured, and the filament wound tube formed thereby is removed from the mandrel.

United States Patent inventors Jack Lowrie McLarty Milwaukee, Wis.;

Charles M. llayes, Hoffman Estates; Edwin J. Latos, Chicago, both of111.

July 29, 1969 Dec. 2 1 197 1 Universal Oil Products Company Des Plaines,lll.

Appl. No. Filed Patented Assignee METHOD OF MAKING SELF-LUBRICATINGFILAMENT WOUND TUBE 19 Claims, 2 Drawing Figs.

US. Cl 156/175, 138/172,156/196,156/289,156/321,156/330 Int. Cl. B65h81/00, B31c 13/00 Field of Search 156/172, 173,187,145, 73, 392, 180,285, 286, 196; 138/172 [56] Relerences Cited UNITED STATES PATENTS3,042,569 7/1962 Paul 156/166 3,158,519 11/1964 Shannon etal. 156/1803,258,379 6/1966 Ponemon et al. 156/175 3,281,299 10/1966 Shobert156/175 3,366,522 1/1968 Underwood. 156/175 X 3,484,317 12/1969Dickerson 156/175 Primary ExaminerCarl D. Ouarforth Assistant ExaminerE.E. Lehmann Auomeys.lames R. Hoatson, Jr. and Philip T. Liggett ABSTRACT:A method of making a filament wound tube having smooth surfaces. Fiberglass filaments are passed through successive resin baths containingparticles of a wear resistant additive. These resin baths are deaeratedto reduce the existence of voids and pits in the resin in the finishedtube. The filaments are flattened and are slowly helically wound in afirst layer onto a mandrel. Subsequent layers are overwound about thefirst layer, the resin is cured, and the filament wound tube formedthereby is removed from the mandrel.

rmmmam 3629.028

SHEET 1 UF 2 Figure INVENTORS: Jack Low/e McL arty Char/es M. HayesEdwin J. Lafos w a? fl n 4m A 7' TOR/V5 Y5 PATENTED DECZI l97l Figure 2SHEET 2 OF 2 l //V VEN TORS- Jac/r Lowr/e McLarfy Char/es M. Hayes BKEdwin J. Lafos ATTORNEYS METHOD OF MAKING SELF-LUBRICATING FILAMENTWOUND TUBE This invention relates to a method of making aself-lubricating filament wound tube. More particularly, this inventionis a method of manufacture in which fiber glass filaments are passedthrough successive resin baths containing particles of a wear resistantadditive. These resin baths are deaerated to reduce the existence ofvoids or pits in the resin of the finished tube. The filaments areflattened and are slowly helically wound in a first layer about amandrel. Subsequent layers are overwound about the first layer, theresin is cured and the filament wound tube formed thereby is removedfrom the mandrel.

Previously, several steps have been required to produce a satisfactoryfilament wound tube having surfaces impregnated with a wear resistantadditive. In one method of producing such a tube, an inner layer ofresin mixed with wear resistant additive is first coated onto a mandrelcoated with a release agent, and the resin is allowed to cure to the Bstage. Thereafter, the coated mandrel is helically overwound with fiberglass filaments. This procedure requires several steps, and substantialtime for initial curing to the B stage is required while the tube andmandrel are positioned in the filamentwinding machine. The multiplesteps required in the manufacture of such a tube are unnecessary, andthe curing of resin to a B stage unnecessarily ties up thefilamentwinding machine and reduces the possible rate of manufactureusing the equipment available.

In another method of manufacturing a self-lubricating filament woundtube, fiber glass filaments are coated with a mixture of resin and wearresistant additive. The fiber glass filaments are immediately helicallywound onto a mandrel, and thereafter the resin cures. The problem withthis construction is that during winding, the resin is so mobile, orfree-flowing, that the fiber glass filaments force their way through theresin to the surface of the mandrel. Also, the air entrapped in theresin and between the resin and the fiber glass filaments causes pits onthe inner surface of the tube. Use of this selflubricating tube as acylinder for a pneumatic piston will shortly render the tubeunserviceable because the piston abrades the fiber glass filaments as itworks back and forth within the cylinder. Once abrasion begins, thecylinder is virtually useless.

In both of these methods of manufacture, the filament wound tubeproduced has a very low coefficient of friction, but the inner surfaceof the tube is not as smooth as it could be. That is, the surface isuneven so that when a piston reciprocates within a tube manufacturedaccording to one of these methods, there is a greater tendency forpressure to leak across the piston than exists in the method ofconstruction described herein. Uneveness of the tube surface has been aproblem in the past because of the pits or craters formed by air bubblesin the resin at the surfaces of the tube which are largely retainedduring curing of the resin.

Furthermore, in all of the previous methods of producing aself-lubricating filament wound tube, air bubbles entrapped within theresin during curing create a weakness in the tube when it is subjectedto various stresses. This occurs because the bubbles create a weaknessin the resin bonds, which are the weakest bonds in the tube.

The primary object of this invention is to produce a selflubricatingfilament wound tube in a single step operation. Neither preliminarycoating of the filaments or mandrel with resin nor subsequent finishingoperations are required to carry out the steps of this invention.

Another object of the invention is to produce a self-lubricatingfilament wound tube having smooth, even surfaces, as well as a lowcoefficient of friction. This is possible because air and other gasbubbles within the resin are driven out of the resin before the resincures. Also, any air bubbles that adhere to the fiber glass filamentsand would otherwise disrupt continuity of the resin coating are alsodriven off prior to curing. As a result, there are no craters or pits inthe surfaces of the tube produced.

An additional object of this invention is to produce a filament woundtube which is stronger than conventional filament wound tubes. Theincreased strength is possible because of the elimination of the air andgas bubbles trapped within the walls of the filament wound tube. Air andgas bubbles trapped within the tube walls present weak points within thetube, and stresses on the tube will rupture the resin bonds at a lowerstress than where there are no voids or trapped gas bubbles in the wallsof the tube.

In a broad aspect this invention is a method of forming a filament woundtube having a smooth inner surface comprising the steps of: coatingfiber glass filaments with resin by passing said filaments through afirst resin bath of a mobile, uncured, liquid, thermosetting plasticresin containing particles of a wear resistant additive; deaerating saidfirst resin bath as said filaments are being coated; passing saidfilaments through a second resin bath of the aforesaid resin and wearresistant additive to coat said filaments; deaerating said second resinbath as said filaments are being coated; drawing said fiberglassfilaments through a constrictive aperture to remove excess resin fromsaid filaments; flattening said filaments by bending said filamentsacross the surfaces of closely spaced guides; heating a mandrel; slowlyhelically winding a first layer of said fiber glass filaments onto saidmandrel; helically overwinding subsequent layers of said filaments ontosaid mandrel; curing said resin, thereby forming a filament wound tube;and removing said tube from said mandrel.

By further restricting the manner of carrying out the steps of thisinvention, a product of even greater quality may be obtained. Forexample, it has been discovered that the filament wound tube produced isof superior quality when the wear resistant additive is graphite,molybdenum disulfide, titanium dioxide, or mica. Graphite, molybdenumdisulfide, and titanium dioxide have previously been used as wearresistant additives in the art of filament winding, and their success iswell known in the art. Mica, however, has been used as a lubricant inother fields, but never as a wear resistant additive in filament woundpipes. Finely divided copper has demonstrated excellent characteristicsin increasing wear resistance by conducting heat from friction away froma tube surface.

An excellent self-lubricating filament wound tube is produced when thethermosetting plastic resin is an epoxy resin. While polyester resinsand other resins may be used, shrinkage is greater in these resins.Since the most common use of such tubing is as apneumatic cylinder, theinner dimensions of the tube are particularly important in order to fallwithin the tolerance of the piston fit. The surface texture of the tubeis improved when deaeration is effected by heating the resin baths,comprised of quantities of resin and wear resistant additive, to atemperature of from about to about 300 F. Heating the resin will reducethe resin viscosity and will produce several favorable results. Airbubbles and gas bubbles more easily escape the resin when it is moremobile, that is, less viscous. Since the air bubbles are driven out ofthe resin baths, they do not become entrapped either at the surface ofthe mandrel or within the walls of the filament wound tube produced. Thedecreased viscosity, or increased mobility, of the resin also hindersthe subsequent entrapment of air bubbles or gas bubbles while the fiberglass filaments are being wound onto the mandrel. As the filaments arefed onto the mandrel, the resin in a more mobile state will fiow ontothe surface of the mandrel or onto the interior layers of filaments andwill thereby preclude air from becoming entrapped beneath the filaments.

An alternative to heating the resin is to deaerate the resin bysubjecting the resin bath to ultrasonic vibrations. Ultrasonic vibrationis created by an ultrasonic generator, which has commonly been used toclean intricate metal parts. When a liquid, such as liquid resin, issubjected to ultrasonic vibration, cavitation is set up in the liquid.That is, tiny bubbles are rapidly generated in the liquid, and just asrapidly collapse. The result is a great impact on any entrained air orother gas in the liquid. This impact tends to driveoff-entrapped gasesfrom the liquid. Ultrasonic vibration need be applied to the liquidresin for only a matter of seconds before the resin is almost completelydeaerated. Ultrasonic vibration is normally applied to the resin at afrequency of from 20,000 cycles per second to 50,000 cycles per second.Below 20,000 cycles per second sound waves are generated which arewithin the upper limits of human hearing and which could be annoying toany persons near by. Above 50,000 cycles per second an inordinate amountof power is required in order to produce the ultrasonic vibration.

It is also helpful if the mandrel is coated with a resin release agentprior to filament winding. Release agents are old in the art of filamentwinding and should be applied where there is any possibility that theresin used might otherwise stick to the surface of the mandrel. Where achromium-steel mandrel is used, no release agent is necessary. For mostother mandrels, a release agent will preclude the possibility that theinner surface of the filament wound tube produced might be damaged uponits removal from the mandrel.

In addition, the mandrel is often heated to a temperature of from about180 to about 300 F. This heating may be from the interior of the mandrelthrough the use of a resistance heating element within the mandrel, orthe heat may be applied from the exterior of the mandrel. In eitherevent, heating is helpful in order to retain the mobility of the resinat the surface of the mandrel as the coated fiber glass filaments arewound onto the mandrel. The heat will also assist in curing the resinand reducing the fabrication time of the filament wound tube.

Using the preferred delivery system in carrying out the method of thisinvention, the first layer of fiber glass filaments is wound onto themandrel at a filament speed of from about to about l0 feet per minute.This speed is slow enough so that air is not entrapped beneath the fiberglass filaments as they are wound onto the mandrel. On the other hand,this speed is not too slow so that the mobile resin drips from themandrel thereby allowing air bubbles to replace the resin on themandrel. The closely spaced guides previously described are preferablyfixed bars, spaced within 4 inches of each other, but the guides mayalternatively be rollers. This close spacing allows the fiber glassfilaments to be flattened as they pass to the distributing arm of thefilament winding machine which helically winds the filaments about themandrel. If the spaced rollers are more distant than 4 inches from eachother the filaments resume a cylindrical shape and air is more likely tobe entrapped beneath the filaments as they are wound onto the mandrel.While all of the filaments may be flattened by being bent across thesurface of the same fixed bar, a different problem is presented whererollers are used. Where rollers are used there must be a separate rollerat each spaced location for each fiber glass filament. Otherwise, thedifference in speed at which the various filaments are drawn onto themandrel will injure fibers being drawn across a single roller rotatingat a fixed speed. Often there are rollers or fixed bars in the resinbaths and the fiber glass filaments pass between the bars or rollers,and the bars or rollers vibrate in the resin baths, thereby furtherassisting in the deaeration of the resin. At the distributing arm, thereis a ring, or toroidal solid through which the filaments pass as theyare distributed onto the mandrel. The filaments are bent across the arcof the ring in the distributing arm to be flattened into a band offilaments. A flat band of filaments is the most desirable configurationin which the filaments are wound onto the mandrel.

Quite often a squeegee is positioned against the filaments as they arebent across the arc of the ring in the distributing arm, thereby furtherreducing the air entrained in the resin on the coated fiber glassfilaments. The squeegee also removes excess resin from the filaments.While a ring is a desirable configuration for the element through whichthe fiber glass filaments pass in the distribution arm, any surface ordistributing means which forms the filaments into a band is acceptable.

The method of this invention is more clearly illustrated in theaccompanying drawings in which:

FIG. 1 is a plan view of apparatus used to perform this invention.

FIG. 2 is a side elevational view along the section lines 2-2 of FIG. 1.

Referring now to the drawings, there is shown a mandrel ll fastened byaxles 2 and 3 to mandrel supports 4 and 5 respectively. Below mandrel 1and along the length of mandrel 1 is located a radiant-heating element41. This heating element 41 may be any type of conventional heatingelement, such as electrical resistance coils, a catalytic heating unit,or hot water. The radiant-heating element ll, depicted as a heatinglaimp, supplies sufficient heat to the surface of mandrel I to maintainmandrel l at a temperature from about l to about 300 F. A reasonablyuniform temperature of the mandrel is maintained since mandrel llrotates during the filament winding process.

A distributing assembly 7 is comprised of upright supports 8 which carryan upper guide portion having two longitudinal rails 42. Rails 42 areparallel to mandrel l and run approximately the length of mandrel I. Adistributing arm 9 traverses the length of the upper guide portion ofdistributing assembly 7, and is confined between the rails 42. Fiberglass filaments are thereby fed onto mandrel 1 from the distributing arm9. Distributing arm 9 is equipped with a ring 10 through which filamentsare fed onto mandrel ll. Ring 10 is positioned so that as filamentscontact ring 10, they are bent across the arc of ring 10 in distributingarm 9 to be flattened into a band of filaments. A squeegee 43 iffastened to the underside of ring 10 and is positioned against thefilaments as they are bent across the arc of ring 10. Squeegee 43removes excess resin from the filaments and reduces the amount of airentrained in the resincoated fiber glass filaments.

On a bench 17 are located two containers or vats l8 and 1.9. Vat 18contains a quantity of resin and particles of a wear resistant additive.This composite mixture will be referred to as resin bath 23. Similarlivat I9 contains a quantity of resin and wear resistant additive whichwill be referred to as resin bath 22. Vat 19 is located atop a vibrationplate of a vibration unit 28 of an ultrasonic generator. This ultrasonicgenerator is comprised of a transducer unit 29 and vibration unit 28interconnected by cable 30. On transducer unit 29 there is located afrequency control 36, a power control 37, and a toggle switch 38, whichturns the unit off and on. When the ultrasonic generator is turned on,crystals within vibration unit 28 vibrate at an ultrasonic frequencyagainst the bottom of vat 19. These vibrations subject resin bath 22 toultrasonic vibration, thereby effecting deaeration of resin bath 22. Thefrequency of ultrasonic vibration is normally at a frequency of from20,000 cycles per second to 50,000 cycles per second.

An alternative method of deaerating a resin bath is employed to deaerateresin bath 23. Vat 18 is positioned in a pan 26 which contains hot oil27. The hot oil 27 is periodically or continuously replaced orsupplemented with additional hot oil through pipe 51 in order tomaintain a temperature in pan 26 sufficient to heat the resin bath 23 toa temperature of from about to about 300 F. Oil may be removed from pan26 through pipe 52. Heating resin bath 23 to this temperature willdeaerate the resin bath and in addition will make the resin bath moremobile, that is, less viscous, in order to effect deaeration. Theincreased mobility of the resin bath 23 has beneficial side effects inthat it reduces the air subsequently entrapped beneath the filaments asthe coated filaments are wound onto mandrel I because a more mobileresin will flow more freely onto mandrel I without allowing air to beentrapped beneath the filaments wound thereon. Either the ultrasonic orthe heating method of deaeration may be employed and the methods ofdeaeration may be used interchangeably. Normally, the same method ofdeaeration will be applied to both of the resin baths 22 and 23, but forpurposes of illustration, the alternative methods are depicted in thedrawings.

The resin in the resin baths 22 and 23 is a mobile, uncured liquid,thermosetting plastic resin, which preferably is an epoxy resin. Anepoxy resin is advantageous in that it shrinks less during curing, andit retains a more stable degree of mobility over a wider temperaturerange than do polyester resins and other resins. The stability ofmobility is desirable because it tends to prevent the resin coating atthe interior surface of a tube formed on mandrel 1 from becoming toothin. Too thin a resin layer will cause the fiber glass filaments tosuffer abrasion when the tube is in use as a pneumatic or hydrauliccylinder. This would occur if the mobility were too great and thetension in the fiber glass filaments forced the filaments through, orpartially through, the inner resin layer during winding. If the mobilityof the resin were not great enough, air would become entrapped beneaththe layers of filament fibers during helical winding of a tube onmandrel 1 and cause internal voids and surface roughness in the tube.

The wear resistant additive used in the resin baths 22 and 23 may be anyof a number of wear resistant additives, such as graphite, molybdenumdisulfide, titanium, dioxide, finely divided metallic copper and mica.These wear resistant additives may be used in combination with eachother or in the altemative with respect to each other as long as noadverse chemical reactions are set up in the resin system used.

The two vats l8 and 19 illustrated in the drawings are necessary becausedeaeration can not be accomplished quickly enough to prevent air bubblesfrom reforming in the resin and adhering to the fiber glass filaments asthey are drawn through the resin if only one vat is used. This isbecause as the fiber glass filaments are initially drawn into a resinbath, bubbles of air are drawn in along with the filaments. As a result,resin bath 22 becomes thoroughly saturated with air bubbles which cannotbe driven off quickly enough for resin bath 22 to be a good resin base.Because the filaments are partially coated with resin from resin bath 22as they enter resin bath 23, less air is entrapped and carried intoresin bath 23. As a result, resin bath 23 is generally less saturatedwith air bubbles and thereby functions as a more suitable resin basewhen coated onto the fiber glass filaments which are wound onto themandrel l. The use of a single vat would be similar to passing fiberglass filaments through resin bath 22 and then directly onto mandrel 1.

Within vats l8 and 19 are located a series of closely spaced fixed barsand 21. These bars are identical in all respects except that the bars 21are positioned on a horizontal plane above bars 20 within each vat. Theends of all of the bars 20 and 21 fit snugly into annular collars 44which are appropriately positioned within each of the vats 18 and 19.Each of the bars 20 and 21 is thereby fixed between a pair of opposingcollars 44. The collars 44 in vat 18 are fastened to the inside walls ofvat 18. Collars 44 instead of being mounted on the walls of the vat 19,are mounted on posts 45 and 46 extending up from the fioor of vat 19. Aseries of short posts 46 extend up to the collars 44 that hold the bars20, and a series of taller posts 45 extend up to the collars 44 holdingbars 21. it can be seen that the bars 20 and 21 in vat 19 will therebyvibrate along with the floor of vat 19 as a result of the ultrasonicvibrations set up in vibration unit 28. As the filaments pass betweenthe bars 20 and 21, the bars 20 and 21 vibrate in the resin bath 22 andthereby contribute even further to the deaeration of the resin bath 22.The vibrating bars 20 and 21 in vat 19 are especially effective inremoving air entrapped next to the fibers passing therebetween. Whilethese bars in vat l9 vibrate in response to the ultrasonic frequencygenerated, a much lower frequency is sufficient to cause the air to beremoved from next to the filament fibers passing between the bars 20 and21.

Between the vats containing the resin baths and the distributingassembly 7 are located a series of closely spaced guides. These guidesare comprised of upright posts between which are mounted pairs of bars.As illustrated in the drawings, two posts 16 are mounted adjacent to vat18. At the upper ends of posts 16 are mounted bars 13 and 14. The fiberglass filaments pass between bars 13 and 14 and are flattened by beingbent across the surfaces of these bars. Similarly,

upright posts 15 are located adjacent to the distributing assembly 7 andhold bars 11 and 12 therebetween. As the resin impregnated fiber glassfilaments pass between bars 13 and 14 and later between bars 11 and 12,the fiber glass filaments are bent first across the surfaces of the bars13 and 14 and then across the surfaces of the bars 11 and 12 so thatthey are flattened. These pairs of bars must be spaced a maximumlongitudinal distance of 4 inches from each other as measured along thefiber glass filaments to fully preserve the flattening effect achieved.

In the filament-winding operation, mandrel 1 is first coated with aconventional resin release agent to facilitate removal of the curedself-lubricating fiber glass filament wound tube produced as an endresult of the method of this invention. Mandrel 1 is thereafter heatedby heating element 41. Several fiber glass filaments 39 are drawn inparallel from a spool 35 which is mounted on a post 34 by an axle 40.The fiber glass filaments 39 are drawn between a series of upright teeth33 mounted at the rear edge of vat 19. The teeth 33, along withsubsequent rows of teeth, guide the fiber glass filaments in asubstantially parallel motion. The fiber glass filaments 39 pass frombetween the teeth 33, beneath a first bar 20 and above a first bar 21.Thereafter the fiber glass filaments 39 pass under subsequent bars 20and over subsequent bars 21. During this time the bars 20 and 21 arevibrating and the resin bath 22 is subjected to ultrasonic vibration bymeans of the ultrasonic generator. The resin bath 22 is therebydeaerated. Deaeration is particularly intense at the fiber glassfilaments 39 as they pass across the bars. The fiber glass filaments 39emerge from the resin bath 22 and pass between guiding teeth 31 mountedat the edge of vat 19. The filaments pass across the gap between vats l9and 18 and through subsequent guiding teeth 32 mounted at the rear edgeof vat 18. The fiber glass filaments 39 pass into resin bath 23 which isheated to deaerate resin bath 23. The resin further coats the fiberglass filaments 39 and the fiber glass filaments 39 are again passedunder bars 20 and over bars 21. Fiber glass filaments 39 emerge fromresin bath 23 and are passed between guide teeth 25 at the front edge ofvat 18. There is a squeegee 24 attached to guide teeth 25 which,together with the edge of vat 18, forms a narrow constrictive aperturethrough which fiber glass filaments 39 are drawn in order to removeexcess resin from the filaments 39. The filaments 39 thereafter are bentacross the surfaces of bars 13 and 14 and bars 11 and 12 and are drawnthrough ring 10 in distributing arm 9. The bars 11, 12, 13, and 14 andthe ring 10 together flatten the filaments 39 into a band 47.Distributing arm 9 slowly travels in the direction indicated by thearrow in F 10. l as mandrel 1 is rotated clockwise, as indicated in FIG.2 at a speed calculated to draw the band 47 of filaments onto mandrel lat a rate of from about 5 to about 10 linear feet per minute. This speedis sufi'icient to prevent resin from dripping from mandrel 1 yet is slowenough so that air does not become entrapped beneath the band 47 as itis wound onto mandrel 1. This slow helical winding is continued whiledistributing arm 9 initially traverses the length of mandrel 1, therebyforming a first layer 49 of resin impregnated wound fiber glassfilaments. Thereafter, subsequent layers of the band of fiber glassfilaments are helically overwound onto first layer 49. This subsequenthelical winding is usually at a greater rate of speed that was the firstlayer of filament winding. After filament winding is complete, filaments39 are cut and the mandrel 1 continues to rotate while the resin coatingon filaments 39 is allowed to cure. This normally takes about an hour atroom temperature, or 1 to 10 minutes using a microwave oven. Thereaftermandrel 1 is removed from mandrel holders 4 and 5 and the filament woundtube produced from the cured layers of resin impregnated fiber glassfilaments is allowed to cure still further for approximately 1 to 2hours if cured by a conventional hot air oven, or for about a day atroom temperature. Thereafter mandrel 1 is removed, and the curedself-lubricating fiber glass filament wound tube is ready for use.

The following examples are further illustrative of the method of thisinvention:

EXAMPLE I 172 parts by weight of an epoxy resin and an anhydride curingagent are mixed with about l7 parts by weight of molybdenum disulfide.Approximately one-half of this mixture is placed in each of two vats.Each of the vats contains a number of spools, or rollers on each ofseveral roller axles. These axles are alternately spaced above and belowthe adjacent roller axles in each vat. The axles are connected by poststo the bottom of the vat, which in turn is subjected to ultrasonicvibrations of 38,000 cycles per second by an ultrasonic generator. Theultrasonic vibration and the vibration of the rollers deaerates theresin bath in each of the vats. A mandrel is heated to a temperature of200 F. and is coated with a conventional resin release agent. Fiberglass filaments are passed through a first vat alternatively under andover the rollers described. Each filament passes over a separate rolleron each roller axle because the speed of travel of each of the filamentsvaries somewhat. The fiber glass filaments are coated with resin andparticles of molybdenum disulfide and emerge from the first vat and arepassed into a second vat through a second resin bath. Again the fiberglass filaments are passed alternately under and over vibrating rollers.The fiber glass filaments are thereby thoroughly coated with resin andparticles of molybdenum disulfide, while the second resin bath isdeaerated by being subjected to ultrasonic vibrations of 38,000 cyclesper second. The fiber glass filaments thereafter emerge from the secondresin bath and are drawn through a constrictive aperture to removeexcess resin from the filaments. The filaments pass from the apertureand are bent across closely spaced guides, so as to become flattened.The filaments thereafter pass through a ring attached to a filamentdistributing arm of a filament winding machine. The filaments are bentacross the arc of the ring and are flattened into a band of filamentswhich is would about the mandrel at a speed of 7 linear feet per minuteto form a first layer of resin impregnated fiber glass filaments on themandrel. Thereafter, the speed is increased and subsequent layers of theband of fiber glass filaments are helically overwound about the firstlayer. After a sufficient number of layers are wound, usually 10 to 12layers, winding of the band of filaments is discontinued. The mandrelcontinues to slowly rotate, however, in order to keep the resin fromdripping off of the mandrel. This slow rotation is continued for aboutan hour during which time the resin cures to form a self-lubricatingfiber glass filament-reinforced tube. The mandrel is removed from thefilament-winding machine, and the tube is allowed to cure still furtheron the mandrel for about 1 hour at 300 F. using a conventional infraredor hot air oven. Thereafter the tube is removed from the mandrel and isready for use.

EXAMPLE ll l72 parts by weight of an epoxy resin and an amine curingagent are mixed with about 17 parts by weight of molybdenum disulfide.Approximately one-half of this mixture is placed in each of two vats.Each of the vats is heated to a temperature of about 220 F. therebydeaerating the resin mixture and rendering the resin mixture moremobile. A mandrel is heated to a temperature of 200 F. and is coatedwith a conventional resin release agent. Fiber glass filaments arepassed through a first of the vats thereby becoming coated with resinand particles of molybdenum disulfide while air entrapped in the resinis driven off by the heat applied therein. The filaments emerge from thefirst vat and are passed into the second of the vats and through asecond resin bath. Again the fiber glass filaments are coated with theresin mixture while the resin mixture is deaerated. The fiber glassfilaments are thereby thoroughly coated with resin and particles ofmolybdenum disulfide. The fiber glass filaments thereafter emerge fromthe second resin bath and are drawn through a constrictive aperture toremove excess resin from the filaments. The filaments pass from theaperture and are bent across closely spaced guides, so as to becomeflattened. The filaments thereafter are fed onto the mandrel as itrotates by a filament distributing arm of a filament-winding machine.The mandrel is rotated at a speed of 9 linear feet per minute to form afirst layer of resin impregnated fiber glass filaments on the mandrel.Thereafter, the speed is increased and subsequent layers of the fiberglass filaments are helicaily overwound about the first layer. After asufficient number of layers are wound, usually 10 to 12 layers, windingof the band of filaments is discontinued. The mandrel continues toslowly rotate, however, in order to keep the resin from dripping off ofthe mandrel. This slow rotation is continued for about 2 hours duringwhich time the resin cures to form a self-lubricating fiber glassfilament reinforced tube. The mandrel is removed from thefilament-winding machine, and the tube is allowed to cure still furtheron the mandrel for about 1 hour at 300 F. using a conventional infraredor hot air oven. Thereafter the self-lubricating filament wound tube isremoved from the mandrel and is ready for use.

EXAMPLE Ill The method of example I is repeated with a polyester resinand a styrene cross-linking agent being substituted for the epoxy resinand anhydride curing agent, and with particles of graphite beingsubstituted for the particles of molybdenum disulfide.

EXAMPLE IV The method of example I is repeated with particles of micasubstituted for particles of molybdenum disulfide.

EXAMPLE V The method of example I is repeated with particles of titaniumdioxide substituted for particles of molybdenum disulfide.

EXAMPLE V1 The method of example I is repeated with particles of finelydivided metallic copper substituted for the particies of molybdenumdisulfide.

The foregoing detailed description and the accompanying drawings havebeen given for cleamess of understanding only, and no unnecessarylimitations should be construed therefrom, as other modifications andvariations will be obvious to those skilled in the art.

I claim as my invention:

1. A method of forming a filament wound tube having a smooth innersurface comprising the steps of:

a. coating fiber glass filaments with resin by passing said filamentsthrough a first resin bath of mobile, uncured, liquid, thermosetting,plastic resin containing particles of a wear resistant additive.

b. deaerating said first resin bath as said filaments are being coated,

c. passing said filaments through a second resin bath of the aforesaidresin and wear resistant additive to coat said filaments,

d. deaerating said second resin bath as said filaments are being coated,

e. drawing said fiber glass filaments through a constrictive aperture toremove excess resin from said filaments, flattening said filaments bybending said filaments across the surfaces of closely spaced guides,

. heating a mandrel,

slowly helically winding a first layer of said fiber glass filamentsonto said mandrel,

. heiically overwinding subsequent layers of said filaments onto saidmandrel,

j. curing said resin thereby forming a filament wound tube,

and

k. removing said tube from said mandrel.

2. The method of claim 1 further characterized in that said mandrel isheated to a temperature of from about 180 to about 300 F.

3. The method of claim 1 further characterized in that deaeration iseffected by heating said resin baths to a temperature of from about 180to about 300 F. v

4. The method of claim 1 further characterized in that deaeration iseffected by subjecting said resin baths to ultrasonic vibration.

5. The method of claim 4 further characterized in that said ultrasonicvibration is at a frequency of from 20,000 cycles per second to 50,000cycles per second.

6. The method of claim 1 further characterized in that said wearresistant additive is molybdenum disulfide.

7. The method of claim 1 further characterized in that said wearresistant additive is graphite.

8. The method of claim 1 further characterized in that said wearresistant additive is titanium dioxide.

9. The method of claim 1 further characterized in that said wearresistant additive is mica.

10. The method of claim I further characterized in that said wearresistant additive is finely divided metallic copper.

11. The method of claim 1 further characterized in that said first layerof said fiber glass filaments is wound onto said mandrel at a filamentspeed of from about 5 to about feet per minute.

12. The method of claim 1 further characterized in that saidthermosetting plastic resin is an epoxy resin.

13. The method of claim 1 further characterized in that said closelyspaced guides are comprised of rollers, spaced within 4 inches of eachother.

14. The method of claim 1 further characterized in that said closelyspaced guides are comprised of bars, spaced within 4 inches of eachother.

15. The method of claim 14 further characterized in that said filamentsare bent across the arc of a ring in the distributing arm of beflattened into a band of filaments.

16. The method of claim 15 further characterized in that a squeegy ispositioned against said filaments as they are bent across the arc of theaforesaid ring, thereby further reducing the air entrained in theaforesaid coated fiber glass filaments.

17. The method of claim 1 further characterized in that there arerollers in said resin baths, and said filaments pass between saidrollers, and said rollers vibrate in said resin baths thereby deaeratingsaid resin baths.

18. The method of claim 1 further characterized in that there are barsin said resin baths, and said filaments pass between said bars, and saidbars vibrate in said resin baths thereby deaerating said resin baths.

19. The method of claim 1 further characterized in that said mandrel iscoated with a resin release agent prior to filament winding.

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2. The method of claim 1 further characterized in that said mandrel isheated to a temperature of from about 180* to about 300* F.
 3. Themethod of claim 1 further characterized in that deaeration is effectedby heating said resin baths to a temperature of from about 180* to about300* F.
 4. The method of claim 1 further characterized in thatdeaeration is effected by subjecting said resin baths to ultrasonicvibration.
 5. The method of claim 4 further characterized in that saidultrasonic vibration is at a frequency of from 20,000 cycles per secondto 50,000 cycles per second.
 6. The method of claim 1 furthercharacterized in that said wear resistant additive is molybdenumdisulfide.
 7. The method of claim 1 further characterized in that saidwear resistant additive is graphite.
 8. The method of claim 1 furthercharacterized in that said wear resistant additive is titanium dioxide.9. The method of claim 1 further characterized in that said wearresistant additive is mica.
 10. The method of claim 1 furthercharacterized in that said wear resistant additive is finely dividedmetallic copper.
 11. The method of claim 1 further characterized in thatsaid first layer of said fiber glass filaments is wound onto saidmandrel at a filament speed of from about 5 to about 10 feet per minute.12. The method of claim 1 further characterized in that saidthermosetting plastic resin is an epoxy resin.
 13. The method of claim 1further characterized in that said closely spaced guides are comprisedof rollers, spaced within 4 inches of each other.
 14. The method ofclaim 1 further characterized in that said closely spaced guides arecomprised of bars, spaced within 4 inches of each other.
 15. The methodof claim 14 further characterized in that said filaments are bent acrossthe arc of a ring in the distributing arm of be flattened into a band offilaments.
 16. The method of claim 15 further characterized in that asqueegy is positioned against said filaments as they are bent across thearc of the aforesaid ring, thereby further reducing the air entrained inthe aforesaid coated fiber glass filaments.
 17. The method of claim 1further characterized in that there are rollers in said resin baths, andsaid filaments pass between said rollers, and said rollers vibrate insaid resin baths thereby deaerating said resin baths.
 18. The method ofclaim 1 further characterized in that there are bars in said resinbaths, and said filaments pass between said bars, and said bars vibratein said resin baths thereby deaerating said resin baths.
 19. The methodof claim 1 further characterized in that said mandrel is coated with aresin release agent prior to filament winding.